FIELD OF THE INVENTION
The present invention relates generally to infectious diseases and, more particularly, to the prevention, diagnosis and treatment of infections caused by gram negative bacteria.
Bacterial sepsis and related septic shock are frequently lethal conditions caused by infections which can result from certain types of surgery, abdominal trauma and immune suppression related to cancer, transplantation therapy or other disease states. It is estimated that over 700,000 patients become susceptible to septic shock-causing bacterial infections each year in the United States alone. Of these, 160,000 actually develop septic shock, resulting in 50,000 deaths annually.
Gram negative bacterial infections comprise the most serious infectious disease problem seen in modern hospitals. Two decades ago, most sepsis contracted in hospitals was attributable to more acute gram positive bacterial pathogens such as Staphylococcus and streptococcus. By contrast, the recent incidence of infection due to gram negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa, has increased.
Gram negative bacteria now account for some 200,000 cases of hospital-acquired infections yearly in the United States, with an overall mortality rate in the range of 20% to 60%. The majority of these hospital-acquired infections are due to such gram negative bacilli as E. coli (most common pathogen isolated from patients with gram negative sepsis), followed in frequency by Klebsiella pneumoniae and P. aeruginosa.
Gram negative sepsis is a disease syndrome resulting from the systemic invasion of gram negative rods and subsequent endotoxemia. The severity of the disease ranges from a transient, self-limiting episode of bacteremia to a fulminant, life-threatening illness often complicated by organ failure and shock. The disease is often the result of invasion from a localized infection site, or may result from trauma, wounds, ulcerations or gastrointestinal obstructions. The symptoms of gram negative sepsis include fever, chills, pulmonary failure and septic shock (severe hypotension).
Gram negative infections are particularly common among patients receiving anti-cancer chemotherapy and immunosuppressive treatment. Infections in such immuno-compromised hosts characteristically exhibit resistance to many antibiotics, or develop resistance over the long course of the infection, making conventional treatment difficult. The ever increasing use of cytotoxic and immunosuppressive therapy and the natural selection for drug resistant bacteria by the extensive use of antibiotics have contributed to gram negative bacteria evolving into pathogens of major clinical significance.
Fortunately, more than a decade ago, investigators in the United States and Germany demonstrated that gram negative endotoxins of many different bacterial genera have a "common core structure." In other words, while many infectious gram negative organisms contain individual capsule and surface polysaccharides, there is a core lipopolysaccharide (LPS) structure that is widely shared among the diverse gram negative bacterial genera and their endotoxins.
This core structure contains material identified as "lipid A" that is felt to be responsible for all of the biologic properties of "endotoxin," including pyrogenicity, activation of the complement and clotting systems, hypotension and death in experimental animals. This core or LPS structure is therefore significant for at least two reasons; its association with endotoxicity and its conservation in gram negative bacterial genera.
Because antibiotic treatment remains largely suboptimal against gram negative sepsis, particularly that associated with P. aeruginosa bacterial infection, (antibiotics are only effective in treating the bacteria and not in reducing the effects of microbial endotoxins) attention has increasingly focused on immunologic methods to prevent and control such infections. Immunotherapy involves the administration of immunoglobulins (antibodies or active fragments thereof) to bolster the host's native defenses against the toxic effects of the bacteria, for example, by enhancing opsonization and phagocytosis of the infecting bacterial cells, or by neutralization of the biological effects of LPS. Antibodies, or active fragments thereof, that bind with the core structure or lipid A, i.e., LPS, could have a broad reactivity with a number of gram negative endotoxins.
Antibodies directed against epitopes or antigenic determinants on the O-specific side chains of smooth gram negative bacteria have limited utility for use in immunotherapy. This is because they are effective against only those strains of bacteria having complementary or cross-reactive antigenic determinants. Such strain-specific antibodies are of only limited utility. While the core oligosaccharide and lipid A of all strains are thought to share antigenic determinants, the few previous attempts to produce and utilize monoclonal antibodies reactive with these regions in Pseudomonas have been largely unsuccessful.
Immunoglobulins that bind most of the clinically significant gram negative pathogens are essential to the success of immunotherapy. P. aeruginosa organisms, which account for 5% to 15% of bloodstream infections, have at least 16 different serotypes (O-antigenic types). Klebsiella organisms have more than 80 capsular types, and E. coli organisms, which are far more common, have more than 130 serotypes.
Patients with bacteremia often do not have a confirmed specific diagnosis as to the type of bacterial infection until bacteriologic results are available, which may take several days. Therapy often must be started based on an empirical diagnosis in order to prevent a patient's condition from rapidly deteriorating during the critical first 24 to 48 hours of illness.
There therefore exists a longstanding need for the production of monoclonal antibodies (MoAb), or active fragments thereof, reactive with an epitope or antigenic determinant present on all important pathogenic strains of gram negative bacteria, thus permitting effective diagnosis, prophylaxis, control of bacterial infection and neutralization of associated endotoxemia attributable to gram negative bacterial genera. It would also be beneficial to have available MoAbs which are cross-reactive with gram positive bacteria useful in the diagnosis, treatment and prevention of bacterial infections generally.